What did early Muslims think of Jesus? Jesus is mentioned many times in the Qur’an. He is described as a righteous prophet chosen by God who performed miracles and continued the work of Abraham and Moses, and he was a sign of the coming Day of Judgment. But Muslims held that Jesus was an apostle only, not God. The Christian doctrine of the Trinity — that there is one God in three persons (Father, Son, and Holy Spirit) — posed a powerful obstacle to Muslim-Christian understanding because of Islam’s emphasis on the absolute oneness of God. Muslims esteemed the Judeo-Christian Scriptures as part of God’s revelation, although they believed that the Qur’an superseded them.

Muslims call Jews and Christians dhimmis, or “protected people,” because they were “people of the book,” that is, the Hebrew Scriptures. Christians and Jews in the areas Muslims conquered were allowed to continue practicing their faith, although they did have to pay a special tax. This toleration was sometimes accompanied by suspicion, however. In Spain, Muslim teachers grew increasingly fearful of close contact with Christians and Jews. Thus, beginning in the late tenth century, Muslim regulations began to prescribe officially what Christians, Jews, and Muslims could do. A Christian or Jew, however much assimilated, remained an infidel. An infidel was an unbeliever, and the word carried a pejorative or disparaging connotation.

By about 950, Caliph Abd al-Rahman III (912–961) of the Umayyad Dynasty of Córdoba ruled most of the Iberian Peninsula. Christian Spain consisted of the tiny kingdoms of Castile, León, Catalonia, Aragon, Navarre, and Portugal. Civil wars among al-Rahman’s descendants weakened the caliphate, and the small northern Christian kingdoms began to expand southward, sometimes working together. When Christian forces conquered Muslim territory, Christian rulers regarded their Muslim and Jewish subjects as infidels and enacted restrictive measures similar to those imposed on Christians in Muslim lands. Christian bishops worried that even knowledge of Islam would lead to ignorance of essential Christian doctrines, and interfaith contacts declined. Christians’ perception of Islam as a menace would help inspire the Crusades of the eleventh through thirteenth centuries (see "What were the causes, course, and consequences of the Crusades?" in Chapter 9).